Trauma-related nightmares (TRNs) are a hallmark re-experiencing symptom of Posttraumatic Stress Disorder (PTSD) and a severe, re-traumatizing source of distress to those with this condition. Proposed research will investigate whether such nightmares might serve as targets for imaginal exposure during prolonged exposure therapy (PE), a first-line treatment for PTSD. Learning and memory of fear extinction are the neurocognitive underpinnings of PE and increased physiological arousal during PE can aid in extinction learning. Thus, PE using TRNs might enhance treatment outcomes because of the greater immediacy and salience of nightmares relative to the more temporally distant traumatic event. Our research group has developed standardized script- driven imagery (SDI) procedures whereby the degree of psychophysiological arousal induced by recollection of the traumatic event that precipitated posttraumatic symptoms (index trauma) can be assessed. Our team has also developed a novel ambulatory device, the NINscan, that can record skin conductance (SC), facial electromyography (EMG) and electrocardiography (ECG) along with simultaneous functional near-infrared spectroscopic (fNIRS) imaging of the lateral prefrontal cortex (LPFC). The LPFC encompasses regions that activate and/or deactivate during SDI in persons with PTSD and includes the right inferior frontal gyrus (rIFG), an area that plays an important role in inhibiting unwanted behavior and cognition and shows reduced inhibitory performance in PTSD. Following screenings that include a structured clinical evaluation establishing PTSD diagnosis and self-report of a least 2 TRNs per week, qualified participants will record an account of their index trauma. They will then complete 2 weeks of sleep diaries and wrist actigraphy with 4 nights of ambulatory polysomnography (PSG), during which they will audio-record, on a time-stamped digital recorder, a detailed nightmare report following any nightmare-induced awakening. A TRN report having sufficient length, clarity and resemblance to the index trauma will be selected and, along with the index-trauma report, will be re- recorded as a script for SDI. Only participants who generated a TRN suitable for SDI (N=40) will then undergo 2 SDI sessions on a single day while wearing the NINscan. One script will be derived from their index trauma and the other from their TRN, the order of which will be counterbalanced across participants. Psychophysiological response and fNIRS LPFC activation will be compared between scripts using 2 primary outcome measures: (1) a validated canonical psychophysiological variable combining SC, EMG and ECG, and (2) script-related activation of the rIFC. We hypothesize that both activations will be greater for the TRN than for the index-trauma script. Exploratory aims will include (1) examination of the sleep stage and electroencephalographic characteristics of sleep preceding awakenings when a nightmare occurred on a night with PSG, and (2) combined PSG and fNIRS recording of trauma-related nightmares using the NINscan in the sleep laboratory in 5 individuals who recorded the most frequent nightmares during home monitoring.